Java String, StringBuffer and StringBuilder Tutorial with Examples

// This is a class with value field and name field.
// When you create this class, you cannot reset the value and all other fields from outside.
// This class does not have methods for the purpose of resetting fields from outside.
// It means this class is immutable
public class ImmutableClassExample  {
   private int value;
   private String name;
   public ImmutableClassExample(String name, int value)  {
          this.value = value;
          this.name= name;
   }
   public String getName()  {
          return name;
   }
   public int getValue()  {
         return value;
   }
}
// This is a class owning a value field.
// After creating the object, you can reset values of the value field by calling setNewValue(int) method.
// This is a mutable class.
public class MutableClassExample  {
     private int value;
     public MutableClassExample(int value)  {
           this.value= value;
     }
     public void setNewValue(int newValue)  {
          this.value = newValue;
     }
}

// Implicit construction via string literal
String str1 = "Java is Hot";

// Explicit construction via new
String str2 = new String("I'm cool");
 

String s1 = "Hello";              // String literal
String s2 = "Hello";              // String literal
String s3 = s1;                   // same reference
String s4 = new String("Hello");  // String object
String s5 = new String("Hello");  // String object

String s1 = "Hello";              // String literal
String s2 = "Hello";              // String literal
String s3 = s1;                   // same reference
String s4 = new String("Hello");  // String object
String s5 = new String("Hello");  // String object

s1 == s1;         // true, same pointer
s1 == s2;         // true, s1 and s2 share storage in common pool
s1 == s3;         // true, s3 is assigned same pointer as s1
s1 == s4;         // false, different pointers
s4 == s5;         // false, different pointers in heap

s1.equals(s3);    // true, same contents
s1.equals(s4);    // true, same contents
s4.equals(s5);    // true, same contents

// Constructors
StringBuffer()             // an initially-empty StringBuffer
StringBuffer(int size)     // with the specified initial size
StringBuffer(String s)     // with the specified initial content

// Length
int length()

// Methods for building up the content
// type could be primitives, char[], String, StringBuffer, etc
StringBuffer append(type arg)  // ==> note above!
StringBuffer insert(int offset, type arg) // ==> note above!

// Methods for manipulating the content
StringBuffer delete(int start, int end)
StringBuffer deleteCharAt(int index)
void setLength(int newSize)
void setCharAt(int index, char newChar)
StringBuffer replace(int start, int end, String s)
StringBuffer reverse()

// Methods for extracting whole/part of the content
char charAt(int index)
String substring(int start)
String substring(int start, int end)
String toString()

// Methods for searching
int indexOf(String searchKey)
int indexOf(String searchKey, int fromIndex)
int lastIndexOf(String searchKey)
int lastIndexOf(String searchKey, int fromIndex)

package org.o7planning.tutorial.strbb;


public class StringBuilderDemo {

    public static void main(String[] args) {
       
        // Create StringBuilder object
        // with no characters in it and
        // an initial capacity specified by the capacity argument
        StringBuilder sb = new StringBuilder(10);
        
        // Append the string Hello ... on sb.
        sb.append("Hello...");
        System.out.println("- sb after appends a string: " + sb);

        // append a character
        char c = '!';
        sb.append(c);
        System.out.println("- sb after appending a char: " + sb);

        // Insert a string at index 5
        sb.insert(8, " Java");
        System.out.println("- sb after insert string: " + sb);
        
    
        // Delete substring at index 5 to 8
        sb.delete(5,8);

        System.out.println("- sb after delete: " + sb);
    }
}